Conveyer mechanism



NOV. 7, 1944. J R| 2,362,305

CONVEYER MECHANI SM Filed Aug. 29, 1939 5 Sheets-Sheet 1 (754w Ha lea Rice NOV. 7, RlCE 2,362,305

CONVEYER MECHANISM Filed Aug. 29, 1939 5 Sheets-Sheet 2 In VenZor: Bl-n Hayley fia'ce Nov. 7, 1944. J. H. RICE 2,362,305

CONVEYER MECHANISM Filed Aug. 29, 1959 5 Sheets-Sheet 5 J. H. RICE 2,362,305 CONVEYER MECHANISM Filed Aug. 29, 1959 s Sheets-Sheet 4 Nov. 7, 1944.

Nov. 7, 1944. H. 5 2,362,305

CONVEYER MECHANISM Filed Aug. 29, 1939 5 Sheets-Sheet 5 42 I) i 45 I ll Inve'kfor:

Jain fluyles Rice y W th Patented Nov. 7, 1944 CONVEYER NIECHANISM John Hughes Rice, Port Eynon, near Swansea, England; assignor to Elmer Manufacturing Co.

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Application August 29, 1939, Serial No. 292,512 In Great Britain September 2, 1938 4- Clahm.

This invention relates to conveyer mechanisms and has for its object to provide an improved mechanism which is particularly applicable to under-feed stokers. The conveyer mechanism is however applicable to other purposes. for operating on material in bulk. form. The mechanism according to the invention comprises essentially a primary ram adapted to convey the material through a primary feed channel which discharges into a secondary feedchannel or channels where a secondary ram or rams effect the further conveyance of the material.

In underfeed retort stolters' for the combustion oi carbonaceous fuels two types of conveyor mechanisms are employed for conveying the fuel from the storage hopper to the retort. When the hopper is mounted; in immediate vicinity to the retort use is. made of a reciprocating ram which advances the fuel. i'rom the hopper and forces it up through the retort to the combustion zone. When however it is necessary to feed the fuel any considerable. distance from the hopper to the retort, it is round that such a reciprocatirrg ram does not operate satisfactorily owing to excessive frictional resistance set up in the cons veying'channel and in such case use is made of a worm conveyer which extends from the hopper to the retort and. serves notonly to convey the fuel from the hopper but also to force it up through the retort. It is found that with some grades' of fuel, particularly friable coals, excessive degradation is always brought about by the grinding actionof the worm, thereby decreasing its'combustion efllciency. Also. such a worm may readily be jammed by hard material wedging between the worm and the housing within which it operates and if such. an accident occurs it is frequently necessary to dismantle the entire apparatus before the obstruction can be removed. This risk of jamming, necessitates the provision of a; siipping clutch, a shear pin or equivalent safety device in the. drive for the worm.

An object of the present invention is to provide a simple and reliable automatic mechanism whereby fuel even of a friable nature can be advanced from a storage hopper situated at a distance from an underfeed retort and delivered into the combustion zone with the minimum expenditure of energy, without appreciable degradation and a complete elimination of any possible risk of the mechanism becoming jammed by fortuitous inclusion of foreign substances with the fuel; also permitting the use of a largely extended range of fuel sizes beyond that possible of employment with a worm conveyer.

In an underfeed stoker mechanism according to the invention a dual ram. mechanism is employed in which one ram operating immediately beneath the storage. hopper, advances the fuel through a diverging channel to an intermediate reception chamber immediately adjacent to the retort; in this chamber and at a point below the delivery from the first ram a second ram operates to feed the retort.

The second rampreferably has a displacement capacity in excess of the first ram to constantly ensure a free and uninterrupted delivery from the first ram. The motion of the two rams derived from a common source is arranged in a manner to develop their respective strokes alternately so that the return stroke of the second ram always provides space in the intermediate reception chamber for the material fed by the forward stroke of the first ram. In this way it is ensured that no substantial resistance is presented to delivery by the first ram and that this first stage of the feed motion is obtained without deterioration of the material. Also by reason of the second ram operating directly at the retort inlet, a point not nearly so approachable with the single ram stoking appliance, the minimum possible resistance is presented to delivery of the material into the retort with resulting relief from degradation in the final stage.

For driving the two rams use is made preferably of an hydraulic arrangement in which a double acting hydraulic piston is formed or mounted on one end of one of the ram plungers, the motion being transmitted to the second ram by means of a gear wheel engaging rack teeth formed in the ram plungers or provided on rack bars secured to the plungers.

A convenient arrangement is to use a constant delivery pump set by means of an adjustable pressure relief valve to an appropriate maximum pressure which for the working stroke of the second ram applies fluid pressure to the entire end surface or the piston, while the return stroke is effected by applying fluid pressure to an annular surface surrounding a reduced portion of the piston which constitutes the connection between the piston and the ram mechanism. As a constant delivery pump is employed the working movement of the second ram will be comparatively slow but with the maximum force while the return stroke will occur at a higher speed with correspondingly smaller force. This is quite satisfactory, as the first stage of the feed movement of the dual ram arrangement meets with very little resistance and so permitting a speed-up of the complete cycle of operation.

The automatic control of the fluid pressure distributing valve for determining the two directions of movement of the piston in the hydraulic cylinder can suitably be derived directly from one of the rack bars. For this purpose a control rod mounted on one of the rack bars is connected to a pilot valve which controls the admission of pressure medium through restricted apertures to" actuate pistons controlling piston valves which place the two sides of the working piston in communication either with the pressure side or with the discharge side. A convenient arrangement is to provide gravity returned actuating pistons for the piston valves. Then when the pilot valve is moved by the motion of the rams to close the inlet for the supply of pressure medium to one actuating piston and to expose the corresponding discharge port, and to expose the inlet for pressure medium to the other actuating piston while closing the corresponding discharge port, the first actuating piston will drop slowly under the action of gravity as the working medium beneath it escapes through the exposed delivery port which is made of such size as to give the desired total period of drop of the actuating piston. After this interval the piston valve will place the corresponding side of the hydraulic cylinder in communication with the pressure conduit to urge the working piston in the opposite direction. Previously, however, the other actuating piston and the other piston valve will have been urged upwardly more quickly by the pressure medium and will have previously cut off the supply of pressure medium to the other side to the working piston and have placed this side of the hydraulic cylinder in communication with the discharge. Thus after the actuation of the pilot valve by the ram mechanism there will be a period of continued movement during which the rams can complete their travel and, after a pause depending upon the difference in the rates of movement of the actuating pistons of the piston valves under the action of the pressure medium and of gravity respectively, the piston in the hydraulic cylinder commences its working stroke in the opposite direction.

The actual rate of operation of the Working piston in the hydraulic cylinder can conveniently be adjusted in such an arrangement by a simple needle valve arranged in the pressure inlet to the distributing valve mechanism. By thus throttling the flow of pressure medium it is possible to vary the rate of operation of the dual ram mechanism within the limits desired in practice without imposing an undue load on the hydraulic pump fitted with pressure relief valve.

With the control valve constructed and operated in the manner described immediate starting of the reciprocating motion of the working piston is obtained from any position of rest and the reversing function of the valve is performed positively at any speed between minimum and maximum as may be determined by adjustment of the throttle valve.

With such a distributing valve mechanism it is convenient for the pump and control valve, the hydraulic cylinder and the rack and pinion mechanism connecting the two rams all to be accommodated in an oil-tight housing the lower part of which constitutes an oil trough from which the pump draws oil and to which oil is discharged from the hydraulic cylinder by way of the distributing valve mechanism.

When applying the invention to underfeed stokers the dual ram system of delivery is suitably applicable to feeding. the conventional form of single retort. Its use will also be found particularly advantageous in feeding a retort arranged with subdivisions by employing a single ram for the first stage which advances the fuel from the storage hopper through a diverging channel to an intermediate reception chamber immediately adjacent to the inlets to the subdivided retort. In this chamber and at a point below the delivery from the first ram, two or more rams, according to the number of subdivisions, yoked to a single actuating rod, operate to perform the second stage of the feed into the respective retort chambers. The advantage of this subdivision of the retort is that the air supplied to the combustion zone through openings or tuyres in the sides and subdividing walls of the retort is much more thoroughly dispersed throughout the fuel bed and accordingly there is complete and uniform combustion obtained over the entire area even with low grade or refractory fuels, which when burnt in a single retort of customary width and fed by either a single ram or worm mechanism gives rise to a black centre where there is substantially no combustion.

Also when employing the dual ram mechanism for underfeed stokers it will be advantageous to provide a single electric motor for driving the pump and the fan supplying the air to the grate. To avoid the noise involved by the use of transmission gearing it is preferred to mount the motor, the pump and the fan in axial alignment either with a common shaft or with their aligned shafts connected by suitable couplings.

It has already been mentioned that the speed of operation of the.ram mechanism can be controlled by means of a simple needle valve. This valve, which will tend to open under the action of the pressure medium, can be held in the desired position by means of an adjusting screw and advantageously a scale is provided adjacent to the adjusting screw showing the setting of the needle valve and thus the resultant rate of operation of the working piston actuating the ram motions. If an automatic control is desired the needle valve can be controlled by means of a cam or equivalent means actuated by a thermostat associated with the boiler or other apparatus heated by the retort. When a battery of retort furnaces is employed each retort will have its own dual ram mechanism but a single oil pump can supply the pressure medium for the ram motions for all the grates. The speed control will of course be separate for each ram motion, whether a hand adjustment or an automatic thermostatic control is provided.

In order that the invention may be more readily understood reference will now be made to the accompanying drawings, in which,

Fig. 1 is a longitudinal section through an under-fed stoker according to the invention,

Fig. 2 is a corresponding plan view with the cover plates removed,

Fig. 3 is a cross section through the retort,

Fig. 4 shows the valve distributing gear in section along the line 44 of Fig. 6,

Fig. 5 is a plan view of Fig. 4,

Fig. 6 is a section along the line li -B of Fig. 4 and,

Fig. 7 a section along the line 1-1 of Fig. 4.

The fuel which is to be fed to the retort I0 is accommodated in the hopper I. This hopper discharges into a primary feed chamber 2 immediately in front of the primary ram 3. By the reciprocation of the ram 3 the fuel is caused to pass through the primary feed duct 2 to the primary delivery chamber 4. The primary feed duct 2 increases progressively in cross section towards the primary delivery chamber 4 so that the resistance to the conveyance of the fuel therethrough is minimized. From the primary delivery chamber 4 the fuel passes to the second ary feed chambers 6 and I, in which operate secthe piston It continues to move in the same direction in the cylinder l'l until the positions of the two pistonvalves 4B, 41 have been reversed, whereupon the piston I6 is caused to move in the opposite direction. In this way the rack bars 12 1 ment and for that purpose the mechanism now to be described is provided in the embodiment illustrated. Secured to the surface of the housing between the free ends of the cylinders 55 and 56 are two brackets 61, 68 carrying a pivot pin 66 on which is mounted a rocker 65 the ends of which carry rollers 63, 64. The stems of the piston valves 46, 41 are provided with extensions BI, 62 which contact with the rollers 53, 54 so that when one of the piston valves 46, 41 is moved by the admission of pressure medium beneath the corresponding piston 51 or 58 the other is positively constrained to move in the other direction. It is then no longer essential for the valve mechanism to be mounted to operate with the piston valves 45, 41 moving vertically. Whether or not the rocker mechanism is provided, the upward movement of the pistons 51, 58 can be limited by a cover plate, indicated at 84 in Fig. 4.

The time period occupied by reversal of the piston valves 46. 41 is primarily established by the relation between the volumetric content of the cylinders 55. 56 and the area of the channels I3, 54 and 59. 60. If so required the time period can be varied by adjustment of needle valves 82, 88 varying the flow of the pressure medium through the channels 53, 54.

The distributing valve mechanism as described above with reference to Figs. 4 to '1 constitutes the subject of my co-pending application, Serial No. 292,513, filed August 29, 1939, and patented June 10. 1941, as Patent No. 2,245,011.

I claim:

1. An underfeed stoker for feeding fuel to a retort, comprising an intermediate chamber outside but adjacent the retort, a hopper remote from said intermediate chamber, an intermediate enclosed passage extending from the hopper to said intermediate chamber for receiving fuel from the hopper and freely discharging it into the intermediate chamber, said passage having a true horizontal bottom and progressively increasing in cross-section from the hopper to the intermediate chamber, a primary ram for feeding fuel from the hopper into the enclosed passage, a secondary ram for feeding fuel from the intermediate chamber to the retort, means connecting the two rams to cause them to move in opposite directions. and mechanism for reciprocating said rams including means for applying greater force at a slower speed to the rams on the feed stroke of the secondary rams than on the feed stroke of the primary ram.

2. An underfeed stoker for feeding fuel to a retort, comprising an intermediate chamber outside but adjacent the retort, a hopper remote from said intermediate chamber, an intermediate enclosed passage extending from the hopper to said intermediate chamber for receiving fuel from the hopper and freely discharging it into the intermediate chamber, said passage havifia true horizontal bottom and progressively iicreasing in cross-section from the hopper to th? intermediate chamber, said intermediate chamber being subdivided, a primary ram for feeding fuel from the hopper into theenclosed passage, a separate secondary ram for feeding fuel from the enclosed passage into each subdivision of the intermediate chamber, means yoking the secondary rams together, and means interconnecting the primary and secondary rams'for causing the primary ram to move in the opposite direction to said secondary rains, and mechanism for reciproeating said rams including-means for applying greater force at a slower speed to the rams on the feed stroke of the secondary rams than on the feed stroke of the primary ram.

3. An underfeed stoker for feeding fuel to a retort, comprising an intermediate chamber outside but adjacent the retort, a hopper remote from said intermediate chamber, an intermediate enclosed passage extending from the hopper to said intermediate chamber for receiving fuel from the hopper and freely discharging it into the intermediate chamber, said passage having a true horizontal bottom and progressively increasing in cross-section from the hopper to the intermediate chamber, a primary ram for feeding fuel from the hopper into the enclosed passage, a secondary ram for feeding fuel from the intermediate chamber to the retort, means connecting the two rams to cause them to move in opposite directions, and mechanism for reciprocating said rams comprising a. cylinder, 9; piston in the cylinder and having a greater effective working area on one sidethan on the other, andmeans for alternately supplying pressure fluid at a constant rate to opposite sides of the piston to cause the piston to move faster in one direction than in theother, and means connecting the piston to said rams to impart a higher speed of travel to the feed stroke of the primary ram than to the secondary rams.

4. An underfeed stoker for feeding fuel to a retort, comprising an intermediate chamber outside but adjacent the retort, a hopper remote from said intermediate chamber, an intermediate enclosed passage extending from the hopper to said intermediate chamber for receiving fuel from the hopper and freely discharging it into the intermediate chamber, said passage having a true horizontal bottom and progressively increasing in cross-section from the h pper to thc'intermediate chamber, said intermediate chamber being subdivided, a primary ram for feeding fuel from the hopper into the enclosed passage, a separate secondary rain for feeding fuel from the enclosed passage into each subdivision of the intermediate chamber, means yoking the secondary rams together, means interconnecting the primary and secondary rams for causing the primary ram to move in the opposite direction to said secondary rams, and mechanism for reciprocating said rams comprising a cylinder, a piston in the cylinder and having a greater effective working area on one side than on the other, and means for alternately supplying pressure fluid at a constant rate to opposite sides of the piston to cause the piston to move faster in one direction than in the other, and means connecting the piston to said rams to impart a higher speed of travel to the feed stroke of the primary ram than .tothe secondary rams.

" JOHN HUGHES RICE. 

